SQL：

Question

我现在一直在努力尝试在我的mysql / mariadb数据库中生成自动聚合代码。我目前正在尝试的方法使用变量。我会事先承认，我不是一个数据库专家。我完全是自学成才，一直在努力为这个特殊问题找到足够的资源。我已经在下面添加了简化的示例，哦，我使用mariadb 10.1。

此代码应该在mysql 5.6以及mariadb 10.0+中运行，我已经在10.1上测试了它并且它可以正常工作。这是我的表格：SQL FIDDLE＆lt; - 由于某种原因不起作用。可能是动态列。如果有人知道原因，我会离开它。

CREATE TABLE data_points
(
  id          BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  device_id   INTEGER,
  dtime       DATETIME,
  sf          INTEGER(11), -- sample frequency or interval
  agg         INTEGER(11), -- aggregation type, actually a fk
  data_point BLOB,
  PRIMARY KEY (id),
  UNIQUE (device_id, dtime, sf, agg)
);

让我们插入一些数据：

INSERT INTO data_points
    (device_id, dtime, sf, agg, data_point)
VALUES
    (1, '2015-01-02 12:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 13:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 14:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 15:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 16:00:00', 1, 60, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));

所以到目前为止一切正常。我试图做的是在不同的时间段内进行聚合，我的最低粒度是60秒。这是我有问题的地方，它可能是显而易见的。

SELECT
  @dp_dtime := MAX(dtime),
  @dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)),
  @dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)),
  @dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4))
FROM data_points
WHERE
  device_id = 1 AND
  dtime BETWEEN '2015/01/02 12:00:00' AND '2015/01/17 23:05:00' AND
  sf = 60 AND
  agg = 1;

INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));

这最终会在语句中的变量所在的位置创建另一行NULL。

select @dp_dtime, @dp_aa, @dp_ab, @pd_ac;
-- This results in NULL, NULL, NULL, NULL

此时我很确定我对变量做错了。这是晚了，14小时的一天。我甚至关闭了吗？有更好/更简单的方法吗？任何帮助将不胜感激。

修改在我的实际用例中，列数取决于正在进行聚合的设备类型。列是优秀的风格＆＃39; aa＆＃39;通过＆＃39; zz＆＃39;可能。虽然我看到的最大值大约是150匝。这可能听起来像一个糟糕的设计，但性能是令人惊讶的，我无法区分这些动态列和实际列之间的区别。（至少只要你不需要为它们编制索引）

Answer 1

可能是一个简单的拼写错误：我看到@_dtime。

在UNIQUE索引中，将dtime放在最后;它会使查询更快。 迷你索引课程：所有=列应该以复合索引排在第一位，任何顺序（基数几乎没有区别）。然后你可以放一个范围＆＃39; （dtime）。范围之后的任何列都不用于过滤。请参阅my cookbook。

摆脱id并将UNIQUE索引提升为PRIMARY KEY;它会使查询更快。 迷你索引课程：辅助密钥（例如您的UNIQUE）需要在密钥和数据之间进行弹跳。 PRIMARY KEY与数据（在InnoDB中）聚集在一起，从而避免了弹跳。相反，范围扫描＆＃39;超过PK是一个范围超过表。

Answer 2

尝试以下查询。

SQL：

CREATE TABLE data_points
(
  id          BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  device_id   INTEGER,
  dtime       DATETIME,
  sf          INTEGER(11), -- sample frequency or interval
  agg         INTEGER(11), -- aggregation type, actually a fk
  data_point BLOB,
  UNIQUE (device_id, dtime, sf, agg)
);
INSERT INTO data_points
    (device_id, dtime, sf, agg, data_point)
VALUES
    (1, '2015-01-02 12:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 13:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 14:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 15:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45)),
    (1, '2015-01-02 16:00:00', 1, 1, COLUMN_CREATE('aa', 12, 'ab', 34, 'ac', 45));
select * from data_points;
SELECT
  @dp_dtime := MAX(dtime) as dp_dtime,
  @dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
  @dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
  @dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
FROM data_points
WHERE
  device_id = 1 AND
  dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
  sf = 1 AND
  agg = 1;
INSERT INTO data_points
(device_id, dtime, sf, agg, data_point)
VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
select * from data_points;

输出：

mysql> select * from data_points;
+----+-----------+---------------------+------+------+----------------------------+
| id | device_id | dtime               | sf   | agg  | data_point                 |
+----+-----------+---------------------+------+------+----------------------------+
|  1 |         1 | 2015-01-02 12:00:00 |    1 |    1 |            aaabacDZ |
|  2 |         1 | 2015-01-02 13:00:00 |    1 |    1 |            aaabacDZ |
|  3 |         1 | 2015-01-02 14:00:00 |    1 |    1 |            aaabacDZ |
|  4 |         1 | 2015-01-02 15:00:00 |    1 |    1 |            aaabacDZ |
|  5 |         1 | 2015-01-02 16:00:00 |    1 |    1 |            aaabacDZ |
+----+-----------+---------------------+------+------+----------------------------+
5 rows in set (0.00 sec)

mysql> SELECT
    ->   @dp_dtime := MAX(dtime) as dp_dtime,
    ->   @dp_aa := MIN(ROUND(COLUMN_GET(data_point, 'aa' AS DOUBLE), 4)) as dp_aa,
    ->   @dp_ab := MIN(ROUND(COLUMN_GET(data_point, 'ab' AS DOUBLE), 4)) as dp_ab,
    ->   @dp_ac := MIN(ROUND(COLUMN_GET(data_point, 'ac' AS DOUBLE), 4)) as dp_ac
    -> FROM data_points
    -> WHERE
    ->   device_id = 1 AND
    ->   dtime BETWEEN '2015/01/02 12:00:00' AND '2015/1/17 23:05:00' AND
    ->   sf = 1 AND
    ->   agg = 1;
+---------------------+---------+---------+---------+
| dp_dtime            | dp_aa   | dp_ab   | dp_ac   |
+---------------------+---------+---------+---------+
| 2015-01-02 16:00:00 | 12.0000 | 34.0000 | 45.0000 |
+---------------------+---------+---------+---------+
1 row in set (0.00 sec)

mysql> INSERT INTO data_points
    -> (device_id, dtime, sf, agg, data_point)
    -> VALUES (8, @dp_dtime, 300, 2, COLUMN_CREATE('aa', @dp_aa, 'ab', @dp_ab, 'ac', @dp_ac));
Query OK, 1 row affected (0.00 sec)

mysql> select * from data_points;
+----+-----------+---------------------+------+------+-------------------------------------------------+
| id | device_id | dtime               | sf   | agg  | data_point                                      |
+----+-----------+---------------------+------+------+-------------------------------------------------+
|  1 |         1 | 2015-01-02 12:00:00 |    1 |    1 |            aaabacDZ                      |
|  2 |         1 | 2015-01-02 13:00:00 |    1 |    1 |            aaabacDZ                      |
|  3 |         1 | 2015-01-02 14:00:00 |    1 |    1 |            aaabacDZ                      |
|  4 |         1 | 2015-01-02 15:00:00 |    1 |    1 |            aaabacDZ                      |
|  5 |         1 | 2015-01-02 16:00:00 |    1 |    1 |            aaabacDZ                      |
|  6 |         8 | 2015-01-02 16:00:00 |  300 |    2 |       ▒  aaabac      (@      A@     ▒F@ |
+----+-----------+---------------------+------+------+-------------------------------------------------+
6 rows in set (0.00 sec)

如何使Mysql变量在查询中工作

2 个答案:

SQL：

输出：